Process of making chemical pulp and apparatus therefor



April 10, 1934. G. L. HELLSTROM 1,954,625

PROCESS OF MAKING CHEMICAL PULP AND APPARATUS THEREFOR Filed Sept. 2, 1932 UNITED STATES PATE-NT PRocEss F MAKING CHEMICAL PULP AND APPARATUS THEREFOR Giusta!I L. M. Hellstrom, Montreal, Quebec, Canada Application September 2, 1932, Serial No.-631,535 In Canada November 4, 1931 4 Claims. (Cl. 92-7 This invention relates to paper making and chips this method of treatment has become feasmore particularly to the process of manufacturible andthe continuous disturbance and circuing chemical pulp and the apparatus therefor. lation of the entire charge of a digester can be In the preparation of chemical pulp the raw carried on with facility.

material, if wood, is rst reduced to the form of A particularly valuable feature of this invensmall chips, or'if of another kind, to pieces of a tion is that it can be readily applied to digesters 00` like size. Large vertical digesters withfconical now installed with comparatively simple alteraends are employed and into these the chips are tions and additions. fed. Chemical liquor is then added and heat is The detail application of the method may be lo supplied to carry out the cooking process. carried out in a variety of arrangements without 'Ihe object of-this invention is to provide imdeparting from the principles on which it is based, 65 provements in this cooking process whereby a` and within the scope'of the invention specified. more uniform and thorough treatment of raw In the description and specication hereafter, material is obtained, with the result that a higher reference will be made to the accompanying and more uniform quality of the product is sedrawing in the form of diagrams, in Which, A

cured, the time required for the process is short- Figure 1 ShOWS a pump Operated tYDe- 7 ened, and great economy both in the quality of Figure 2 ShOWS aSeIeW Operated typeliquor required 4and the Yamount of steam em- Figure 1 shows adigester 1 of the type comployed is gained, and screening losses are reduced monly adopted in the Sulphite DreeeSS et the Dresto a minimum. ent time.

Further objects and advantages will be set This has an inlet 10 atthe t0n through Which 75 forth hereinafter. the chips or material to be treated are admitted.

Hitherto a large number of patents have been It has the outlet 11 at the bottom leading to the taken out covering a variety of efforts to improve blow valve 12 and blow pipe 13 through which the the cooking process. Most of these relate to cooked pulp is removed when the treatment is methods 0f Circulating the liquor contained in completed. Connected to the outlet 11 isasecond 80 the digester. .The liquor has usually been drawn valve 14and large pipe 15 leading to a pump out of the digester at one or more points and 2 driven by amOtOI 20- FlOm the Dump 2 a Simi with or without reheating has been fed back at lar large pipe 21 leads upwards' t0 a bend 22 with other points. Screens have been employed to a valve 23 and second inlet 24 in the upper conprevent the lwithdrawal of the material being ical end of the digester 1. Auxiliary steam jets 85 treated, and the blocking up of these screens b'y 3 may be provided to the pipe 15, pipe 21 and solid matter has been a constant source of troubend 22. The outlet 11 also has a valved steam 1 ble. l The packing of the vmaterial in the lower feed pipe and there may be Steam inlets at part of the digester has also been a cause of inthe top of the digester but which are not shown. efficiency. 1 Surrounding the digester may be one or more 90 By means of this invention, these and other manifolds 6 with a series of small inlets 60 through objections to the liquor circulating methods are the wall of the digester. Thesemanfolds 6 have obviated. It consists briey in not only withsteam feed pipes 31 whereby` a series of steam drawing the liquor but also a portion of the ma,- jets may\be forced into the charge of the diterial being treated and returningthem again ges'ter through the inlets 60. There may also be 95 to the digester. l valved `connections 25 between the pipe 21 and By thus causing a gradual movement and disthe manifolds 6. These connections have screened turbance of the entire chargeof the digester, the openings into the pipe 21, whereby only uid liquor is able to penetrate the charge uniformly, can pass into the manifolds 6.

Y* completely and more rapidly, the heat applied Figure 2 shows a digester 1 of similar type with 100 acts throughout the digester at more even temelle 01 more large pipes 21 With bends Opening peratures, there is no clogging or packing 0f the into the digester adjacent to the inlet 10 and outsolid portion of the charge, there are noscreens let 11 at 24 and 27,Y Where the pipe enters the or similar obstructions within the digester, to belOWer part 0f the digester, a mOtOI driven rotatcome blocked and seriously affect the cooking ing screw 28 operates to draw a portion of the process, and the treatment of the entire charge is charge into the pipe 21 and force it upwards and l lmfolfm and COmDI-eteback into the'digester 1 at the top through inlet Owing to the recent development of pumps 24.

that could handle solids of the nature of wood In Figure 1 means are provided whereby steam may be injected into the mass at suitable points to maintain the proper temperature and assist in the mixing or agitation of the mass. Means are also provided whereby some of the liquor passing upwards may be returned to the digester at lower levels than the main return inlet.

The flow of the material through the pipes may be aided and accelerated by means of steam jets 3 at various points.

By means of windows 8 in the pipes 15 and 21 forming inspection points the progress of the cooking can be accurately observed and valuable information obtained as to the effects of varied treatments, in addition to that obtained by the usual control apparatus.

In the types shown in Figures l and 2 the pipes 21 may be provided with steam jackets 7 as shown in Fig. 2 whereby the heat of the cooking may be maintained during the passage of the mass from the bottom to the top of the digester.

By means of such construction the charge of the digester consisting of chips and liquor is kept in a state of continuous movement and agitation whereby the liquor is enabled to penetrate the mass uniformly and the heat maintained throughout the digester at the required temperature.

By such treatment the product will be of a high standard of uniform quality and uneven cooking obviated. The rapid penetration of the liquor throughout the mass will expedite its action on the mass and the duration of the cooking will be greatly reduced.

By means of the process there will be a higher yield and a saving in raw material, liquor and steam. Owing to the saving in time occupied in a cooking, the output of a digester will be increased. The cooking will be under-more accurate control than has hitherto been possible by the systems now in operation. Ineiicient digesters can be readily converted into highly efficient apparatus at small capital outlay.

It is obvious that this circulation of the charge of the digester might be reversed, and that the ow through the pipes be made to run from the upper part of the digester to the lower part.

In the usual practice of filling a digester, the raw material is fed into the top and the cooking liquor is then pumped into the bottom of the digester, this results in the formation of a bridge of the raw material a short distance above the main outlet. In order to vary and control the height or level at which such a bridge will form, a suitable quantity of liquor is rst pumped into the bottom of the digester before it is filled with the raw material. This bridge will provide a screening medium for the cooking liquor and the amount of raw material to be withdrawn with the liquor in the circulation of the charge can be regulated and the necesssary disturbance and mixing of the contents can be controlled.

I claim:

1. An apparatus for cooking fibrous material comprising a digester, a conduit arranged eX- ternally of the digester for leading chips and cooking liquor from one end of the digester to the other end of the latter pumping means interposed in said conduit for pumping the liquor and chips therethrough, and means in the conduit between one end of the digester andthe pump to cle'ar the conduit between the last mentioned end of the digester and the pump and to feed said pump.

2. An apparatus as claimed in claim 1 in which the last mentioned means comprises a pipe for directing a jet of steam into the conduit in the direction of iow of the liquor and chips from the digester toward the pump.

3. An apparatus as claimed in claim 1 in which the last mentioned means comprises a motordriven rotating screw.

4. An apparatus for cooking fibrous material comprising a digester adapted to contain cooking liquor and wood chips, a conduit arranged externally of the digester and leading from one end of the digester to the other end of the latter, pumping means interposed in the conduit vfor forcing cooking liquor and chips from the lower end ofthe digester to the upper end of the digester, means in the conduit between the lower end of the digester and the pumping means for clearing the conduit and feeding the pumping means, and means inthe conduit between the pumping means and the upper end of the digester for clearing the conduit between the pumping means and the upper end of the digester and for assisting in feeding the liquor and chips from the pumping means into the digester.

GUSTAF L. M. HELLSTROM. 

